The production of high pressure laminates is well known, having been carried out for many years. Generally, the procedures for forming such laminates involve providing phenolic (i.e. phenol-formaldehyde) resin impregnated paper core sheets and melamine (i.e. melamine-formaldehyde) resin decorative and overlay sheets, and pressing the stacked resin impregnated sheets under heat on the order of 230.degree.-310.degree. F. and under pressure of approximately 800-1600 psi until the resins have become thermoset, thereby providing an extremely hard, attractive and permanent surfacing material known as a "high pressure laminate" meeting NEMA Standards. These high pressure laminates have, for many years, found use as counter and table tops, bathroom and kitchen work surfaces, furniture and cabinet surfacing, wall paneling and partitionings, doors, etc.
Most general purpose decorative high pressure laminates, of about 1/16 inch thickness, are formed of an assembly comprising a top ply of .alpha.-cellulose paper, about 20 lbs. ream weight, impregnated with a partially cured water solution of melamine-formaldehyde condensate; a print ply therebeneath, normally also an .alpha.-cellulose paper, pigment filled, with or without decorative printing on the surface thereof, ranging in weight from 50 to 125 lbs. ream weight and also impregnated with a partially cured amino resin condensate, usually the same melamine resin as used in the overlay ply; and therebeneath a plurality (e.g. six) core plys which are normally 100-130 lb. ream weight kraft paper, impregnated with a water or alcohol soluble partially cured phenolic resin condensate. All of such partially cured resin condensates are referred to as being in the "B-stage"; in this stage they are thermoplastic and will flow under heat and pressure during the high heat, high pressure laminating procedure.
The above described assembly is repeated, back-to-back with a separator, each two laminates being separated by a pressing plate die, until a "book" containing, typically, 10 assemblies is obtained. The book is inserted in a high pressure press, and the laminates are cured under the conditions of heat and pressure indicated above. During the pressing cycle, the resins flow and cure, consolidating the individual plys and forming a comprehensive and infusible cross-linked product. After cure, the book is removed from the press and the laminates are separated, trimmed, and their backs or bottom surfaces sanded to improve adhesion for subsequently gluing to various substrates.
In the early years, generally only glossy surface laminates were produced (i.e. using polished molding surfaces), though some attempts were made to provide laminates with some slight surface irregularities to give satin or "textured" finishes. In more recent years it has become increasingly desirable to provide various types of irregular surfaces, ranging from relatively shallow depressions such as textured (e.g. satin, matte, or semi-gloss) surfaces, to relatively deeply "sculptured" or embossed surfaces which have a noticeable three-dimensional effect, such as wood grain, leather, slate, abstract patterns, creative designs, etc. Particularly with the rising costs of natural products, it has become more desirable to provide deeply sculptured high pressure laminates which simulate natural materials such as wood, leather and slate.
Today, high pressure decorative laminates meeting NEMA standards are manufactured with smooth glossy surfaces, with textured surfaces, or with deeply sculptured or embossed surfaces. In the latter case, a textured surface is usually superimposed on the embossed surface, and these textured surfaces are normally obtained by utilization of a release, parting or separating membrane or sheet of known type which is located, during the laminating operation, between the upper surface of the uppermost laminate and the molding plate die. In the production of deeply sculptured surfaces which simulate natural products such as slate, leather and wood, it is particularly desirable that the textured surfaces be superimposed over the face of the simulated product, since this provides a softer and more naturally appearing product.
In the manufacture of deeply embossed or sculptured surfaces having surface depth variations as great as 7 mils which duplicate natural products such as slate, leather, wood and the like, it has in the past generally been necessary to use either extremely expensive etched steel or stainless laminating die plates or, alternatively, thermoset pressing plate dies such as described in the Michaelson et al U.S. Pat. Nos. 3,303,081 and 3,311,520. While the use of such dies provides the necessary embossing, many simulated natural products, such as wood grain, must have appropriate color in registry with the surface embossing or debossing. Unfortunately, the problem of registration of color and embossing has proved very difficult, conventional registry techniques such as used in the printing industry being unreliable on a consistent basis in the manufacture of high pressure laminates, and also being extremely expensive, often involving complex electronic sensing equipment.
Other methods of providing laminates having registered color and texture have utilized valley printing, namely the inking of high portions of an engraved plate and pressing into the resin while curing. This operation, as well as the mechanical registration of an embossing roll or plate with a print, is difficult to carry into production and/or does not always give a uniform product. In addition, inks may not be compatible with or as durable as the base resin in which case the product will not meet NEMA Standards.
In more recent years, a number of other techniques have been developed in an attempt to solve the problems of registration of color and embossing in the manufacture of deeply sculptured high pressure laminates. Certain of these techniques have been found to be highly useful in the preparation of certain specific types of configuration, e.g. see U.S. Pats. Nos. 3,700,537 and 3,698,978. Other recent techniques have been more versatile from the viewpoint of the design of the product (note, e.g., U.S. Pat. Nos. 3,814,647; 3,732,137; 3,802,947; and 3,661,672), but some of these recent techniques have been less than fully desirable because they require special materials and/or are difficult to carry out successfully with the result that the products are sometimes inconsistent or the manufacturing operation is more expensive than is desirable.
In co-pending application, Ser. No. 528,776, there is disclosed a method which involves using, in place of the conventional overlay sheet, a light weight overlay sheet which is impregnated with melamine resin containing finely ground pigment. During the simultaneous embossing and laminating using a three-dimensional press plate acting against such overlay sheet, the resin and pigment in the overlay flow laterally from the high pressure areas to the low pressure areas with the result that the underlying print sheet is visible through the overlay sheet in the high pressure areas while the pigment in the overlay sheet in the low pressure areas masks the print sheet. This technique gives highly realistic products of a generally mottled nature, such as simulated leather, but the variation in colors which is possible using this technique is somewhat limited.